It is often the case in orthodontic practice that crowdings in the upper and lower dental arch or other orthodontic problems such as protrusion are overcome by extracting first or second bicuspids or molars to create space and then moving the surrounding teeth into that remaining space. Controlled tooth movement is brought about by first cementing orthodontic bands with welded-on hooks around the teeth to be moved and similar bands on the first molars or other teeth acting as anchors. Tooth moving forces are, in present practice, created by attaching springs or elastic cords between the hooks (on the cheek side) in front of and behind the extraction site. One problem with this technique is that reactive forces will cause unwanted movement of the molar or other anchor teeth and the loss of control of the process. The reactive force on the first molars may be reduced, but not controlled, by banding and linking them to the second molars behind them. The present invention controls the above mentioned forward molar movement without the need for additional banding.
A major use of the invention can be found when second molars are extracted in preference to the more visable first and second premolars bicuspids and then moving the first molars and other forwardly positioned teeth backward into the created spaces as dictated by the particular dental needs of the patient. Molars are difficult to move in a backward direction. Solutions to the problem of finding suitable backward molar forces have involved external harnesses which use the neck or cranium (cervical straps, head gear or combinations of these). Although the backward molar forces thus obtained are adequate, the arrangement is bulky, unsightly and uncomfortable. Patient cooperation is therefore difficult to obtain. As an alternative to the external apparatus mentioned above, backward forces have been obtained by utilizing the unyielding, tissue-covered basal bone in particular areas just behind the upper and lower front teeth (in the area of the root tips). This can be done through an upper (maxilliary) palatal pad resting on the highest, most frontal portion of the palatal vault above the roots of the front teeth or a similar pair of pads resting on either side of the frenum of the tongue in the area of the root tips of the lower front teeth.
Perhaps the best known of these appliances is the "Nance Holding Arch". In this passive device a palatal pad molded of acrylic plastic is used. Imbedded in the plastic are heavy wires which extend to and are soldered to orthodontic bands. The latter are then cemented to back teeth such as the upper first or second molars. During the necessary laboratory assembly of the holding arch, the wires are joined to the tongue side of the orthodontic bands and are made of such length as to allow the pad to rest on the palate when the appliance is installed. The Nance device has no mechanisms to move molars backwardly or to control their forward movement.
Another removable anchoring appliance was invented by Bedell for the lower teeth. This anchorage is held in place by wire clasps connecting it temporarily to various teeth and by vertical posts inserted into vertical tubes on the tongue side of affixed orthodontic bands. It is necessary to custom fabricate the Bedell appliance in a laboratory for each patient. It is a removable appliance (by the patient) and thus requires his full cooperation.
An additional appliance used for anchoring in the upper or lower dental arch is the "lip bumper". In its simplest form the lip bumper consists of a padded, horse-shoe shaped wire installed with its pad resting between the lip and the front teeth but separated from the latter and maintained at a given distance during usage to produce limited backward pressure on the posterior teeth. With the ends of the wire inserted into tubes on the cheek side of orthodontic bands on first or second molars, lip pressure is transferred to backward molar movement by preventing the wires from freely sliding through their respective molar tubes through the use of mechanical stops. The device produces limited dental movement, is uncomfortable, produces an unsightly protrusion of the lower or upper lip and may cause unwanted forward movement of the incisors.